ABUJA, Nigeria (AP) — Three men entered a central Nigerian church just before Bible study began, but instead of joining the worship service they opened fire, killing at least 19 people in an attack that shows that violence is spreading in the divided nation.

Witnesses and the military described a chaotic, blood-soaked scene at the Deeper Life evangelical church in Otite, a quiet neighborhood on the outskirts of the city of Okene, 250 kilometers (155 miles) southwest of Nigeria’s capital, Abuja.

Two gunmen sprayed the windowless sanctuary Monday night with fire from Kalashnikov assault rifles, said Lt. Col. Gabriel Olorunyomi, the head of a local joint army and police unit.

Another armed man stayed back and switched off the generator providing lights in the church, leaving those inside unable to flee as the gunfire flashed through the darkness, witness Lawan Saliu said. Saliu, who suffered gunshot wounds to the stomach, spoke from a hospital bed Tuesday.

No group claimed responsibility for the attack, but the violence came as Nigeria is facing attacks from a radical Islamist sect known as Boko Haram.

Olorunyomi said 15 people died in the church and four died later from their injuries. He said the number of wounded remained unknown, but that some of them sought care in hospitals, while others remained at home. A rescue official, who spoke on condition of anonymity, said that probably fewer than 20 people were wounded in the attack.

Soldiers and police officers searched for gunmen through Monday night, but had made no arrests on Tuesday, said Kogi state police spokesman Simon Ile.

Later on Tuesday, three gunmen on a motorcycle shot at a military patrol vehicle in Okene, said Olorunyomi. Police said two soldiers were killed in the attack.

Boko Haram, whose name means “Western education is sacrilege” in the Hausa language of Nigeria’s mostly Muslim north, has attacked churches in the past. The sect has also has attacked mosques. However, Boko Haram has not previously claimed responsibility for attacks on places of worship this far south.

The national chief of police, Mohammed Abubakar, said in a statement Tuesday that he has ordered a 24-hour surveillance of all places of worship in the central state of Kogi state, which has not suffered such attacks.

In April, however, authorities there raided a bomb factory run by suspected sect members. They also blamed Boko Haram for a February prison break in the Kogi town of Koton-Karifi that freed 119 inmates. That attack mirrored a massive prison break in the northeastern city of Bauchi in September 2010 when Boko Haram freed about 700 inmates.

The sect is blamed for more than 660 killings this year alone in Nigeria, according to an Associated Press count.

Nigeria, a nation of more than 160 million people, is divided between a predominantly Muslim north and mainly Christian south. While members of the two faiths often live and work together, and intermarry, Boko Haram attacks have increased religious tensions in the nation over the last year.